Shepherd’s Bush IV, London, England. (Gisela Erlacher)

As cities grow and develop more rapidly than ever before, it's hard to think there are still "leftover" spaces hidden among the urbanized landscapes of the world. But that's exactly what Austrian architectural photographer Gisela Erlacherfound wedged between the massive megastructures of countries such as China, England, the Netherlands and Austria.

Erlacher traveled to several cities to capture—and uncover—life in the overlooked spaces under bridges, highways and overpasses. The results are collected in a book "Skies of Concrete," a photographic exploration ofpeople's ability to live, work, and play in what might seem like the most inhospitable and unusual of places.

"There are countless publications on bridges and highways, and a lot of impressive images of beautifully entangled highway interchanges from bird’s eye view. But I was interested in the bottom-up perspective—the view of a passer-by—and the ways of life that can be discovered down there," Erlacher told Fast Company.

(MORE: World's Weirdest Bridges)

Some of the surprising "under spaces" Erlacher found in her travels contained not only housing, parking, and storage, but also skate parks, tea houses, and food stalls "in varying shades of legality." In Chongqing, China, she photographed cafes and lunch spots under the criss-crossing expressways. In London, England, an overpass spans over an urban horse paddock; and under a railway bridge in the Austrian Alps, an unconventional ropes course features chains and pieces of wood.

Erlacher's photographs show how much change landscapes have experienced as cities make way for roadways and modes of transportation. But they also show how resourceful people can be, creating ways to take advantage of disused spaces to make sure life goes on.

"Skies of Concrete" is available from Park Books. To view more of Gisela Erlacher's work, visit her website.